A lot of people seem to be having problems getting Apple's X11 version to work with their international keyboards. Skimming the web, I found this to be a good way of solving it (part of it taken from some mandrake linux forum):

Run XDarwin or OroborOSX and have it use your language.keymapping file.

In a terminal, do the following:

% xmodmap -pke .yourlanguage.xmodmap

Quit XDarwin and run X11.app

In a terminal, run:

% xmodmap .yourlanguage.xmodmap

You should now have a working international keyboard! If this works, you can make it run every time you start X11 by adding the following line to your .xinitrc file:

You can find an app at VersionTracker fixing this in an elegant way.
http://www.versiontracker.com/moreinfo.fcgi?id=17831&db=mac

As the Product Description says:
X11 Launcher may be of some use to people like me with a non-US keyboard who want to use the just released (as of 01/10/2003) Apple X11 beta. It allows selecting the desired keyboard layout for X11, as well as giving some extra command line parameters. This app should become obsolete quickly, as Apple improve its application. The source code is available.

I also just noticed that /etc/X11/xinitrc (no period there) seems to be a basic .xinitrc to use. I copied it to ~ and made some modifications so that it xmodmap's my keyboard (I renamed my dvorak keyboard to .Xmodmap and it uses it by default) and didn't start the various apps listed at the end of the file. Oh, and I had it start up quartz-vm too.

Not on all international keyboards
Authored by: dani++ on Jan 13, '03 03:36:07PM

Well, that particular trick does not apply to Spanish keyboards as the system-supplied Espanol.keymapping did not work on XDarwin on the first place.

I did build an xmodmap file by hand (thanks to the helpful 'xve' command that prints X11 events to STDOUT). This worked like a charm on XDarwin and I promptly forgot about the issue. The problems begin using Apple's X11 as it does not seem to recognize some char symbols ('periodcentered' for example) and specially does not recognize the 'Alt' modifier key. Issuing a 'xmodmap -xpm' prints the modifier key setup:

I copied francais.keymapping to ~/Library/Keyboards/USA.keymapping and it gives
me grosso modo a French keyboard. X11 Launcher seems to do the same thing
and with its extra bells and whistles, it is pretty nice. What seems to be missing
(or I'm not astute enough to have uncovered them) are various essential characters
for unix, like |, ~, {, }, and so forth. I'd be appreciative of a fix for that, while awaiting
Apple's ultimate solution. For the moment, I'm limited to opening a Darwin terminal
and copying them from there. A fairly inefficient solution but one of desperation....

I am new to the Mac OS X world but have used unix for a long time. The problem I am finding in trying to use international characters in OroborOSX has apparently nothing to do with the keyboard. For example, if I do:

xmodmap -pke > .xmodmap.default

and I look at the output I see that:

keycode 16 = c C ccedilla Ccedilla

However, when I try to type at the command line in an xterm the key combination Alt+c what I get as an screen output is C' , not ç.

I have already included in my .Xdefaults the line:

xterm*utf8: 1

so that unicode characters should be displayed and indeed they are when I do a ls -lav of a directory with filenames such as Imágenes. However, when I use the Tab to complete the filename what I get is Ima\314\201genes instead of Imágenes.